Kinetic and thermodynamic control of C(sp 2 )–H activation enables site-selective borylation

Abstract

Catalysts that distinguish between electronically distinct carbon-hydrogen (C–H) bonds without relying on steric effects or directing groups are challenging to design. In this work, cobalt precatalysts supported by N -alkyl-imidazole–substituted pyridine dicarbene (ACNC) pincer ligands are described that enable undirected, remote borylation of fluoroaromatics and expansion of scope to include electron-rich arenes, pyridines, and tri- and difluoromethoxylated arenes, thereby addressing one of the major limitations of first-row transition metal C–H functionalization catalysts. Mechanistic studies established a kinetic preference for C–H bond activation at the meta -position despite cobalt-aryl complexes resulting from ortho C–H activation being thermodynamically preferred. Switchable site selectivity in C–H borylation as a function of the boron reagent was thereby preliminarily demonstrated using a single precatalyst.